This invention relates in general to axially adjustable driveshaft assemblies, such as are commonly used in drive train systems. In particular, this invention relates to an improved structure for such an axially adjustable driveshaft assembly and to a method of installing same in a drive train system.
Drive train systems are widely used for generating power from a source and for transferring such power from the source to a driven mechanism. Frequently, the source generates rotational power, and such rotational power is transferred from the source to a rotatably driven mechanism. For example, in most land vehicles in use today, an engine/transmission assembly generates rotational power, and such rotational power is transferred from an output shaft of the engine/transmission assembly through a driveshaft assembly to an input shaft of an axle assembly so as to rotatably drive the wheels of the vehicle. To accomplish this, a typical driveshaft assembly includes a hollow cylindrical driveshaft tube having a pair of end fittings, such as a pair of tube yokes, secured to the front and rear ends thereof. The front end fitting forms a portion of a front universal joint that connects the output shaft of the engine/transmission assembly to the front end of the driveshaft tube. Similarly, the rear end fitting forms a portion of a rear universal joint that connects the rear end of the driveshaft tube to the input shaft of the axle assembly. The front and rear universal joints provide a rotational driving connection from the output shaft of the engine/transmission assembly through the driveshaft tube to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment between the rotational axes of these three shafts.
Not only must a typical drive train system accommodate a limited amount of angular misalignment between the source of rotational power and the rotatably driven device, but it must also typically accommodate a limited amount of relative axial movement therebetween. For example, in most vehicles, a small amount of relative axial movement frequently occurs between the engine/transmission assembly and the axle assembly when the vehicle is operated. To address this, it is known to provide a slip joint in the driveshaft assembly. A typical slip joint includes first and second members that have respective structures formed thereon that cooperate with one another for concurrent rotational movement, while permitting a limited amount of axial movement to occur therebetween.
One type of slip joint that commonly used in conventional driveshaft assemblies is a sliding spline type of slip joint. A typical sliding spline slip joint includes male and female members having respective pluralities of splines formed thereon. The male member is generally cylindrical in shape and has a plurality of outwardly extending splines formed on the outer surface thereof. The male member may be formed integrally with or secured to an end of the driveshaft assembly described above. The female member, on the other hand, is generally hollow and cylindrical in shape and has a plurality of inwardly extending splines formed on the inner surface thereof. The female member may be formed integrally with or secured to a yoke that forms a portion of one of the universal joints described above. To assemble the slip joint, the male member is inserted within the female member such that the outwardly extending splines of the male member cooperate with the inwardly extending splines of the female member. As a result, the male and female members are connected together for concurrent rotational movement. However, the outwardly extending splines of the male member can slide relative to the inwardly extending splines of the female member to allow a limited amount of relative axial movement to occur between the engine/transmission assembly and the axle assembly of the drive train system.
In order to facilitate relative axial movement between the male and female splined members, a certain amount of clearance is provided between the mating splines provided thereon. However, a relatively large amount of clearance between the mating splines is undesirable because it results in looseness between the male and female splined members. Looseness that occurs in the rotational direction of the splined members, wherein one of the splined members can rotate relative to the other splined member, is referred to as backlash. Looseness that occurs in the axial direction of the splined members, wherein one of the splined members can extend at a cantilevered angle relative to the other splined member, is referred to as broken back. To reduce the adverse effects of such looseness, it is desirable that the amount of clearance provided between the mating splines of the male and female splined members be minimized.
Unfortunately, when the amount of clearance provided between the mating splines of the male and female splined members is relatively small, the magnitude of the force that is required to effect relative axial movement of the male and female members is relatively large. Although this relatively large magnitude of force is usually not of any consequence during normal operation of the drive train system, it can make it relatively difficult to initially install the driveshaft assembly in a drive train system. During such installation, the distance separating the source of rotational power from the rotatably driven mechanism is usually fixed. Typically, however, the driveshaft assembly has a length that is often different from the fixed distance separating the source of rotational power from the rotatably driven mechanism. Thus, to install the driveshaft assembly in the drive train system, the length of the driveshaft assembly must usually first be adjusted to correspond with the distance separating the source of rotational power from the rotatably driven mechanism.
In the past, this initial relative axial movement of the male and female members of the driveshaft assembly to facilitate installation has been accomplished manually by the person or persons who have been tasked to install the driveshaft assembly within the drive train system. However, as noted above, the magnitude of the force that is required to effect relative axial movement of the male and female members can be relatively large, making such manual extension or retraction difficult. Thus, it would be desirable to provide an improved structure for an axially adjustable driveshaft assembly, and a method of installing same in a drive train system, that avoids these problems.